Process for the production of homogeneous rubber deposits from rubber latex



Patented July 2-1, 1931 UNITED, STATE s PATENT OFFICE FRANCIS GABOR AND PAUL KLEIN, F BUDAPEST, HUNGARY, AND ANDREW SZEGVARI, 0F AKRON, OHIO, ASSIGNORS, BY MESNE ASSIGNMENTS, TO AMERICAN ANODE, INC.,

A conromrron or DELAWARE PROCESS FOR THE PRODUCTION or Ho oGENEoUs RUBBER nnrosn's FROM RUBBER LATEX No Drawing. Application filed July 22, 1926, Serial No. 124,285, and in Germany September 4, 1925,

In specification of the Patent No. 1,548,689 we have stated thatin the production of rubber deposits by electrophoretic means electrolysis of the electrolytes contained in the 5, dispersion liquid of the rubber latex takes place simultaneously with the deposition of the rubber, gas being developed at the anode and we have further stated that it is. owing to this anodic generation of gas that homoeneous rubber deposits cannot be obtained in this manner. This recognition led to the proposal made in the specification of the aforesaid patent, to enable the gases set free at. the anode to escape by spacially separating the point of production of the anodic gases from the point of formation of the rubber deposit. This spacial separation was efi'ected by means of a porous base which was interposed as depositing base,-

between the anode and the cathode. In the specification of our application No. 35,246, filed June 5, 1925, we specified further means for enabling homogeneous precipitates to be obtained or for obviating the detrimental infiuence of the electrolytic separation of gas at the anode, which consisted in su pressing the liberation of gases: This was e ected by employin in the electrophoretic device sub stances a apted to prevent the liberation of gases and more particularly by employing anodes which contain substances or are composed of substances adapted to combine the anodic gases in anysuitab-le manner in order to enable homogeneous rubber precipitates to be produced also-immediately upon the sure face of electrically conductive anodes.

We have foundthat .all metallic anodes, even for example lead or zinc anodes which it might be assumed would enter into chemical combination with the gases liberatedthereupon by electrolysis. and would consequently by com oxfygen, prevent the liberation of gas, ofier di culties in preventing the development of gas on the anode and in producing from latex preserved in the usual commercial way, completely homogeneous, precipitates.

We have now ascertained that when em plo ing metallic sufli deposition bases, it is not cient merely to select a suitable metal ining'with these gases, especially the 1 for the anode but that the prevention of the development of gases at the anode with certainty, in order to produce homogeneous caoutchouc deposits also depends on the quality of the corresponding preliminary treatment of the commercial latex. We have especially found that commercial preserved latex contains substances, in the presence of which the formation of gases at theanode under the influence of the electric current is favourably influenced and that these substances must be removed from the latex to be electrophoretically treated for the production of rubber goods, or must be reduced to harmless proportion. The removal or decrease of the detrimental substances can for example be effected by the partial or entire removal or by partial or entire transformation of same into a harmless form.

I Commercial preserved latex contains for 70 example 0.51% ammonia. We have found that the greater part .of this ammonia must be removed. Experiments have shown that when treating latex containing"33% rubber and employing anodes of zinc, cadmium, lead and similar metals or alloys'thereof it is advantageous to reducethe ammonia content of the latex (33% rubber content) to a total alkalinity of about 0.09 normal ammonium hydroxide solution or below. On the other hand however it has been found that for the quality of the homogeneous rubber deposit obtained and for'the behaviour of the latex, it is advantageous not to remove the ammolnia content entirely. The upper limit and the most advantageous proportion .of the ammonia content depend on the condition and the concentration of the latex employed, the temperature, the substance of the anode and on other circumstances, and must always be ascertained by experiments.

The decrease .or removal of the preventing agents can be effected by dialysis or by Washing out the latex, for example by concentrating same by centrifuging and subsequent di lution.- Such operations may also efiect the removal or decrease of other constituents of the latex which might also favour the development ofgases at the anode or might for other reasons, otherwise detrimentally infill '100 ence the process or the quality of the product.

If the substance to be removed is volatile, as is the case for'example with the ammonia at present generally employed, the amount thereof may also be diminished by evaporation, aeration, or by heating or by employing these measures simultaneously. Experiments have shown that the ammonia content can be reduced to the required small amount, for example by heating the latex to about C. for some hours without endangering the same.

Another method of eliminating or diminishing or removing the preserving agent consists in transforming the same into a compound which does not tend to form gas or any otherwise detrimental compound during the electrophoretic deposition of the rubber. Thus for example the ammonia content of the commercial preserved latex can be counteracted by formaldehyde or its polymers, in which case the ammonia is transformed into hexamethylentetramine and hydroxyl ion concentration is correspondingly reduced. Other carbonyl-containing CO compounds can be employed in the same way.

Another method of transforming the detrimental substances in case they should be alkaline, consists in merely neutralizing them, in which case however limits are set to the addition of strongly acid substances, by the danger of coagulation. Nevertheless the acid required for the neutralization can frequently be produced in the latex itself (for instance by the oxidation of aldehyde).

Another possibility of avoiding the formation of gas consists in employing for preserv ing latex, instead of ammonia, other alkaline acting substances which do not incline to the formation of gases at all during the electrophoretic deposition of the rubber or which may be employed only in such small amounts that they do not produce any formation of gas during the electrophoretic depo sition.

Instead of alkaline additions, substances having a strongly germicidal action such as for .example thymol or the hydrocupreine compounds known as Eucupinotoxine and vucine may be employed for preserving the latex in which case such small amounts are sufficient that they do not come into consideration for the electrolytic gas-formation.

Even if the ammonia preserved latex has been freed of its ammonia-content to the lowest admissible extent prior to treatment, it is generally preferable to add to the latex a disinfectant whiclrdoes not'produce any detrimental gas formation.

With latices prepared in the above described manner perfect completely homogeneous rubber deposits can be obtained directly on zinc, cadmium, iron and lead anodes as well as uponanodes which consist of certain alloys containing the above metals (for example an alloy containing 90% zinc and 10% antimony).

The experiments hitherto made appear to indicate, although this has not been definitely ascertained, that the above described behaviour of the latex depends on the circumstance that on the one hand electrodes have to be employed which, in the course of the electrophoretic deposition of the rubber under the given conditions or in the presence of the electrolytes employed are continuously ionized, being for example dissolved by the oxidation products produced by the electrolysis of the metal of the anode and that on the other hand the concentration of the electrolyte supplying the hydroxyl ion in relation to the rate of dissolution of the anode or of the oxidation products formed from the anode metal is reduced to such an extent that it is merely suflicient for secondary reactions and the hydroxyl ions are unable to effect a primary discharge which would lead to the formation of gases.

The decrease in concentration of the gasforming electrolyte by diluting the latex does not lead to the result because commercial preserved latex had to be diluted to a six or seven fold extent for this purpose and it is impos sible to produce from such a diluted latex suitable rubber deposits since the same do n t exhibit a smooth surface, and moreover the speed of deposition of the rubber is considerably decreased.

\Ve have also found that even in the pres ence of substances inducing gas formation for example of the ammonia contained in commercial preserved latex, it is possible to suppress the formation of gases if the electrophoresis is commenced at a current density at which the jump in potential at the anode is insufficient to effect electrolysis with its attendant gas formation that is to say beldw about 1.7 volts. As the electrophoretic deposition of the rubber progresses the electrical resistance may be increased. In this case the voltage can be gradually increased without increasing the jump in potential at the anode. In this process however the formation of the deposit proceeds extremely slowly' and the thickness of the non-porous layer appears to be very greatly limited.

The condition of the .rubber deposit formed directly on the surface of the metal anode can be influenced in an undesirable manner by the too immediate influence of the metal entering into solution from the anode for which I'BHSOIlIit may be advantageous to provide the anode with a liquid absorbing non-metallic protection as for example a thin coating of tanned or untanned gelatine, collodion, and the like which is adapted to prevent the direct contact of the rubber with the metal. This liquid-absorbing coating which is however impermeable to gas bubblesmust be saturated prior to dipping the anode into the latexfwitlrany suitable meing to a substantial extent in the commercial diumj adapted favourably to influence the rubber latex substances tending to liberate coagulation of the rubber in the given argases at the deposition base, immersing in rangement. The surface of the anodesmay the treated latex a deposition base comprisbe smoothed or may be provided with any ing a metal or alloy substantially incapable desired raised or sunk pattern.- The individunder the influence of a rubber depositing 11211 parts of the anodic surface may consist electric current of'forming gases thereon in of metals upon which formation of gas the treated latex, and passing through said ours and upon which a correspondingly polatex and deposition base an electric current insulating coating.

rous deposit is accordingly produced. Porcapable of electrophoretically depositing tions of the anode on which no deposit is rubber from saidlatex at said base. desired may be provided with an electrically 2. The process set forth in claim lin which the deposition base is composed of metals Moreover individual portions of the depocapable of continuously ionizing during the sition base may consist of porous substances electrophoretic deposition.

permeable to liquid and arranged in front 3. The process set forth in claim 1 in which i of the anode in the manner described in the the deposition base comprises a metal of a 1 surface of the anode.

specification of Patent No. 1,548,689 whilst class including zinc cadmium, iron, lead and at the remaining portions of the deposition alloys of these meta s.

base, the deposit is formed directly upon the 4. The process of making homogeneous rubber deposits from commercial rubber In other respects the deposition when uslatex by electrophoretic deposition which ing metallic deposition bases offers similar comprises eliminating to a substantial extent possibilities to those described in the specifiin the commercial rubber latex substances cationof Patent No. 1,548,689 in connection tending to liberate. gases at, the deposition with. the deposition upon porous non-conbase and adding to the treated latex preservaccelerators, colouring matters and other ducting bases i. e. various additional sub-- ing agents substantiallyineapable of liberstances for example vulcanizing agents, vulating gas at the deposition base during eleccanizing accelerators, filling materials, 001- trophoretic deposition, immersing in the ouring matters and the like may be mixed treated latex a deposition base comprising a with the latex, the deposit may be-produced metal or alloy substantially incapable under upon moulds entirely immersed in the latex the influence of a rubber depositing electric or upon endless bases (drums or bands) passcurrent of forming gases thereon in the ing through the latex in a continuous manner treated latex, and passing through such and in both cases fibrous materials or fabric treated latex and deposition base an electric insertions can be employed or saturated with current capable of electrophoretically derubber. w positing rubber from said latex at said base.

When employing metallic moulds the rub- 5. The process as set forth in claimA in ber deposit can be dried and vulcanized upon which the preserving agents comprise a subthe moulds themselves or the deposit obtained stance of a class capable of retarding .bac-,

can be removed from the moulds prior to terial action in the latex. vulcanization, since the deposits produced by 6. The process of making homogeneous means of the above-described process posrubber deposits from ammonia-preserved sess sufficient strength and elasticity for this latex by electrophoretic deposition which p p comprises reducing the ammonia concentra It should be remarked that the expression 'tion in the latex to such an extent that subrubber latex is intended to denote vulstantiallyno gas formation takes place at canized or unvulcanized latex both free from the deposition base during electrophoretic filling materials as well as containing filling deposition, immersing in the treated latex a materials, vulcanizing agents, vulcanizing deposition base rcomprising-a metal substantially incapable under the influence of an electrophoretic depositing current of forming gases thereon and passin through such additional substances.

- It should be well understood that the above described electrophoretic deposition process treated' latex and deposition ase an electric can be advantageously carried-outwith the 1 current capable of electrophoretically de-, auxiliary means described in 'the' specificapositing rubber from said latex at said base. tions of our co-pending applications Nos. 7. The process of making homogeneous 35,199 and35,246, filed. June 5," 1 9 25. rubber deposits from ammonia-preserved Having now particularly des'efbed and latpx by electrophoretic deposition which ascertained the nature of our sai'iljinvention comprises reducing-the ammonia content in and-1n what manner same 1s to be-performed, "the latex to a 0.1 normal solution or below,

we declarethat what we claim is immersing in the treated latex a deposition 1. The process of making by electricmeans base comprising a metal substantially incahomogeneous rubber deposits from common 'pable under the influence of an electrophore cial rubber latex which comprises elimina'ttie depositing-current of forming gases there-' rubber deposits from ammonia-preserved latex by electrophoretic deposition which comprises reducing the ammonia content of 1 the latex by adding to the latex a substance reacting with the ammonia, immersing in the treated latex a deposition base comprising a metal substantially incapable under the influence of an electrophoretic depositing current of forming gases thereon and passing through such treated latex and deposition base an electric current capable of electrophoretically depositing rubber from said latex at said base.

9. The process of making homogeneous rubber deposits from ammonia-preserved latex by electrophoretic deposition which comprises reducing the ammonia content of the latext by adding thereto subustances capable of reducing the alkalinity thereof, immersing in the treated latex a deposition base comprising a metal substantially incapable under the influence of an electrophoretic depositing current of forming gases thereon and passing through such treated latex and deposition base an electric current capable of electrophoretically depositing rubber from said latex at said base.

10. The process of making homogeneous rubber deposits from ammonia-preserved latex by electrophoretic deposition which comprises reducing the ammonia content of the latex by adding an aldehyde thereto, immersing in the treated latex a deposition base comprising a metal substantially incapable under the influence of an electroph-oretic depositing current of forming gases thereon and passing through such treated latex and deposition base an electric current capable of electrophoretically depositing rubber from said latex at said base.

11. The process of making homogeneous rubber deposits from ammonia-preserved latex by electrophoretic deposition which comprises reducing the ammonia content of the latex by adding formaldehyde thereto, immersing in the treated latex a deposition base comprising a metal substantially incapable under the influence of an electrophoretic depositing current of forming gases thereon -and passing through such treated latex and deposition base an electric current capable of electrophoretically depositing rubber from said latex at said base.

12. The process of making homogeneous rubber deposits from preserved rubber latex which comprisesreducing the total alkalinity of the latex to a 0.1 normal solution or below,

- bringing a deposition base in contact with the treated latex, and depositing a layer of rubber 65 from the latex on the deposition base.

13. The process of making homogeneous rubber deposits from preserved rubber latex which comprises adding to the latex a substance capable of reducing the alkalinity of the latex, bringing a deposition base in contact with the treated latex, and depositing a layer of rubber from the latext on the deposition base.

1 1. The process of making homogeneous rubber deposits from preserved rubber latex which comprises adding an aldehyde to the latex, bringing a deposition base in contact with the treated latex, and depositing a layer of rubber from the latex on the deposition base.

15. The process of making homogeneous rubber deposits from preserved rubber latex which comprises adding formaldehyde to the latex, bringing a deposition base in contact with the treated latex, and depositing a layer of rubber from the latex on the deposition base.

16. The process of making homogeneous rubber deposits from latex preserved with ammonia or amines which comprises reducing the total alkalinity of the latex by addition of substances reacting with the ammonia or amine, bringing a deposition base in contact With the treated latex, and depositing a layer of rubber from the latex on the deposition base.

17. The process of making homogeneous rubber deposits from latex preserved with ammonia or amines which comprises adding an aldehyde to the latex, bringing a deposition base in contact with the treated latex, and depositing a layer of rubber from the latex on the deposition base.

18. The process of makinghomogeneous rubber deposits from latex preserved with ammonia or amines which comprises adding formaldehyde to the latex, bringing a deposition base in contact with the treated latex, and depositing a layer of rubber from the latex on the deposition base.

In testimony whereof we afiix our signatures.

FRANCIS GABOR. PAUL KLEIN. ANDREW sZEGVARI. 

